Our long-range goal is to understand the neural mechanisms of hearing. All information about sound is encoded by patterns of activity in the auditory nerve. By virtue of its position as the obligatory recipient of auditory nerve input, the cochlear nucleus is a key site to study how acoustic stimuli are translated into neural codes that are then sent to the brain. Cochlear nucleus neurons are organized into definable groups that share common inputs, cellular mechanisms, and axonal targets. By linking structure and function for different cell types, we seek to understand their roles in hearing. Ultimately, this kind of knowledge should allow us to interpret structural anomalies resulting from deafness or noise-induced damage in terms of their effect on acoustic processing. In this application, we propose to study multipolar cells in the ventral division of the cochlear nucleus. The axons of these cells target other neurons in the cochlear nucleus. They also project to nearly every brain stem and midbrain structure in the auditory pathway. Multipolar neurons are comprised of several distinct subclasses of cells. We will use pathway tracing and immunocytochemical techniques to study the structure and neurochemistry of different classes with respect to their axonal targets. We will employ an in vitro preparation of the isolated whole brain to study how the activity within a subclass influences its axonal targets. Information obtained from both types of experiments will result in links between structural and functional data for different cell types. This combined anatomic and physiologic approach to the study of multipolar cells will allow us to determine how their encoded messages are distributed in the brain, will impact models of binaural hearing, and may suggest new designs for human brain stem implants.